Author Topic: Which battey for my robot ?? (Read 6442 times)

s80ts0465 · « **on:** November 22, 2007, 06:06:00 AM »

This my first robot project and i would like to limit more than possible the errors

i use four 24Vdc motor, microntroller OOPic with 6-15Vdc, and WiFi system with 5Vdc-9Vdc.

So many different voltage. Moreover i need to create an autocharger robot, so the robot must understand when and where charging the battery. On this way i think that is better to have only one voltage battery and even better only one battey.
On this way i think to use a lead-acid battery of 24V (or 2 of 12V in serial).

But on the net i found that normally are used the NiCad or NiMh battery ad not the lead-acid battery even if they costs less than the other. Why?
What type of battey do you suggest me to use? are the acid-lead battery ok to use with the robot??

Many thanks
Bye bye Ste

Joe · « **Reply #1 on:** November 22, 2007, 10:24:11 AM »

Sounds like you're building a pretty big robot to be using 4 24V motors and to even consider lead acid batteries. I can't say I've tried them because NiMH have always done the trick for a decent price and without the weight of a brick, perhaps that's why they are commonplace on the "homebrew robotics" websites. Also, you don't have to order them online if you don't want to wait around cause you can buy them at any RC hobby store.

Also there is an issue of motor noise and massive voltage spikes when you stop or change directions suddenly. These will be travelling right down the same power bus that goes to your microcontroller. This can require some trial and error (error being ruined microcontrollers) to fix which is more feasible if are using a $3 Pic or AVR than a $60 OOPic. You may want to consider a separate small battery pack, 6 - 9V for your electronics (6V only if all your regulators can handle the low dropout, otherwise 7.2V min). I personally don't recommend "9V"s. They have ridiculously low current capacity. If you are bold and don't mind blowing stuff up and have more money than you know what to do with you can just use one 24V pack and regulate it down to 6V with a switching regulator.

As for the autocharger, I have a strong feeling you may be getting in over your head and might suggest the $50 robot so you can get a feel for what your trying to accomplish. If you can do this project your talking about, the FDR should be easy.

Admin · « **Reply #2 on:** November 22, 2007, 10:49:40 AM »

The advantage of using NiHM and NiCad over lead acid is that they store more energy for less weight. They recharge much faster than lead acid, too.

Heavy batteries are just bad for a whole host of reasons. Lead acids also have trouble supplying large amounts of current.

As for your motors, 24V is a lot! A lot meaning that carrying 24V of batteries just adds a lot to your robot weight (again, a bad thing).

If possible, go down to 12V motors, and hence 12V batteries.

Now as Joe said, you will need a voltage regulator to power your microcontroller and WiFi. Basically just plug in the 24V, and it outputs a nice clean 5V. But there is a problem in that voltage regulators dissapate heat to do this.

(24V - 5V) * current = wasted_power

Current is probably going to be ~.2A, meaning 3.8W of wasted heat. Some voltage regulators cannot handle more than 20V, and many cannot handle above ~2W, so check the datasheets just to be sure.

s80ts0465 · « **Reply #3 on:** November 23, 2007, 02:13:27 AM »

ok i'll look for some 12V motor (which do you suggest me?where to buy them

)

About the switching regulator from 24V to 5V-9V i think to buy this one http://www.superdroidrobots.com/shop/item.asp?itemid=761 that should work fine with these powers.

About the fact to use different battery, one for motor and one for electronic, i've chosen to use only one battery with the same voltage considering the fact i want to crate the autocharging dock, and it's easier if you have only one voltage line (at least i think so). Otherwise i should use more than one charging line for each single voltage; one line to charge the 7.2V line, one for 12V and one for 24V for example.

In this days that i was looking for about which is the better battery for my project, i've considered the fact that my robot should stay for a long time connected to the docking station and once a day go around for about 20minutes (max 1h i think). Considering this strange application of my robot, i've to use a battery that works fine being almost always connected to the charging line. In fact the lead acid battery has the float charge that can be applied for an unlimited time instead the float charge doesn't exist for the other types of batteries. So with my working condition i'd ruin the NiMH batteries that doesn't like to stay alwasy under charging state.
What do you think about my consideration? does it have a sense?? is it correct or do you think i can use the NiMh battery as well??

Thanks a lot
Bye Ste

Admin · « **Reply #4 on:** November 23, 2007, 05:49:32 AM »

Quote

ok i'll look for some 12V motor (which do you suggest me?where to buy them )

http://www.societyofrobots.com/robot_parts_list_motors_servos.shtml

As for your other question . . . so all batteries can only be recharged a certain number of times until failure. Check the datasheets. A lithium battery is probably best for what you describe, as its great for being recharged mid-state. You will need a special charger for that . . .

You need to also determine your current draw, because chances are your lead acid's wont be able to handle it.

s80ts0465 · « **Reply #5 on:** November 23, 2007, 07:24:55 AM »

Quote from: Admin on November 23, 2007, 05:49:32 AM

As for your other question . . . so all batteries can only be recharged a certain number of times until failure. Check the datasheets. A lithium battery is probably best for what you describe, as its great for being recharged mid-state. You will need a special charger for that . . .

But if i constastly continue to charge the lithium battery (23hours for days and sometimes also longer, so many consecutive days), the battery are gotten ruined faster than normal, isn't? This is the main reason i think that for my case the lead acid batteries are better, but obviously if you tell me that exist a fload/stand-by voltage for the lithium battery as well, most probably i'll buy them!
Is it possible to constantly connect a lithium battery to the AC/DC convert withou any problem to ruin the battery???

Quote from: Admin on November 23, 2007, 05:49:32 AM

You need to also determine your current draw, because chances are your lead acid's wont be able to handle it.

Oh well, it's possible to buy many different type of acid lead, for example i could even take one with 7000mAhr or more.

Bye Ste

Admin · « **Reply #6 on:** November 23, 2007, 07:41:20 AM »

Quote

if i constastly continue to charge the lithium battery (23hours for days and sometimes also longer, so many consecutive days), the battery are gotten ruined faster than normal, isn't?

This is true for all batteries, no exceptions. Check the datasheets.

Quote

Is it possible to constantly connect a lithium battery to the AC/DC convert withou any problem to ruin the battery???

What you will want is the charger to auto-detect when the battery is fully charged, then cut off power. Most chargers on the market already do this for you.

Quote

Oh well, it's possible to buy many different type of acid lead, for example i could even take one with 7000mAhr or more.

Thats mAh, not mA.

mAh represents how much power can be supplied total before your battery is drained, while mA is current supplied at any given instant. Your battery can have a million mAh, but if it can only supply 1mA at any time, your motors will never work.

s80ts0465 · « **Reply #7 on:** November 23, 2007, 08:21:16 AM »

Quote from: Admin on November 23, 2007, 07:41:20 AM

Quote
Is it possible to constantly connect a lithium battery to the AC/DC convert withou any problem to ruin the battery???
What you will want is the charger to auto-detect when the battery is fully charged, then cut off power. Most chargers on the market already do this for you.

Ok. that's right. And when the voltage comes lower than a voltage the charger starts to charging once again ù8as the cellphone charger

), but is it to consider as a cycle?? because if it's a cycle i'll have to change too often the battery

considering that at least 1 time for day the charger will start to charge the battey

Quote from: Admin on November 23, 2007, 07:41:20 AM

mAh represents how much power can be supplied total before your battery is drained, while mA is current supplied at any given instant. Your battery can have a million mAh, but if it can only supply 1mA at any time, your motors will never work.

Ok now i've understood what you meant, but it think that this isn't a problem for a lead acid battery that usually is able to sopport many Ampere spike a supply some A at any time, egual or a bit less than the max discharging current, or not?

Admin · « **Reply #8 on:** November 23, 2007, 08:25:29 AM »

Again, check the battery datasheet and determine what your current draw is. All your answers are right in front of you.
(I cant stress this any more!

)

s80ts0465 · « **Reply #9 on:** November 23, 2007, 08:40:59 AM »

i'm sorry to bug you

anyway here the datasheet : http://www.power-sonic.com/site/doc/prod/88.pdf

and it's wrote that for 1 hour rate the battery support 4.5A to 9V. The main trouble seems the drop to 9V !!!!

Anyway do you suggest me to use lithium battery even if i've to mantain almost always the battery connected to the charger ??

Bye

Admin · « **Reply #10 on:** November 23, 2007, 08:21:15 PM »

there are lots of batteries to choose from
but how about one of these 12V NiMH batteries?
http://www.onlybatterypacks.com/items.asp?db=37

I'm willing to bet it has about ~500+ charge cycles on it (Im too lazy to look up the datasheet), meaning for under a $100 you get a battery that lasts 1 to 2 years of daily charging.

and a NiMH 12V peak charger (peak meaning it cuts off power when batteries are fully charged):
http://www.onlybatterypacks.com/items.asp?db=12

nottoooily · « **Reply #11 on:** November 23, 2007, 11:36:02 PM »

Yep, lead acid is easy for leaving it on, but you can do this with any battery if you have an intelligent enough charger. It depends how much design work you want to put in and if it really matters to get that maximum life out of a battery. I've heard that you can leave NiMH on charge continuously as long as the current isn't enough to cause heat damage. Something like 100mA for a 2500mAhr battery is supposed to be OK.

Don't worry about voltage spikes from motors getting into the power supply, the battery will flatten them out. It's the switching transistors which can be at risk. I think using two batteries is an ugly and difficult unneccesity.

I made a robot with a 7Ahr SLA once and it was a complete crapout when the motors had a heavy load (carrying the battery

) Of course you could design it better.

On the other hand one of those batteries can drive a ride-on robot if you don't mind damaging it's life and huge voltage sags.

A downside is that owning a lead acid battery is a bit like owning a puppy, you have to make a long term commitment to maintain it otherwise it'll die.

Quote

Oh well, it's possible to buy many different type of acid lead, for example i could even take one with 7000mAhr or more.

Bye Ste

s80ts0465 · « **Reply #12 on:** November 24, 2007, 07:52:31 AM »

Ok after your suggests i've finally decided to leave the SLA battery and limit the choice between NIMH and lithium.
From what i've found on the net and also on this website, the lithium batteries are better for life, n° of cycle, weight but more expensive.

I've found this lithium battery that i really like :
http://www.powerstream.com/Pli.htm
what do you think about it?? I'd have many differnt output voltage and diffrente charging voltage.

Which battery type do u prefer between NIMH and lithium (don't consider the price) ??

Thanks bye
Ste

Admin · « **Reply #13 on:** November 24, 2007, 09:04:05 AM »

Quote

I've found this lithium battery that i really like :
http://www.powerstream.com/Pli.htm
what do you think about it?? I'd have many differnt output voltage and diffrente charging voltage.

are you sure thats the correct link? those coin size batteries couldn't even power a squirrel robot

remember that lithium batteries require a special charger.

Quote

Which battery type do u prefer between NIMH and lithium (don't consider the price) ??

I bought a whole bunch of NiCads and NiMH 5 years ago and still use them . . . never had a need to buy new batteries . . .

s80ts0465 · « **Reply #14 on:** November 24, 2007, 11:27:18 AM »

ops sorry.
Tha's the correct linkl: http://www.powerstream.com/PST-MP3500.htm
what do you think about it?

bye

ed1380 · « **Reply #15 on:** November 24, 2007, 11:43:14 AM »

Quote from: s80ts0465 on November 24, 2007, 11:27:18 AM

ops sorry.
Tha's the correct linkl: http://www.powerstream.com/PST-MP3500.htm
what do you think about it?

bye

holy shiznit thats awesome

bit expensive though

s80ts0465 · « **Reply #16 on:** November 24, 2007, 01:42:42 PM »

fortunately i don't pay

but it's in my interest it's really the best thing for my project!

Admin · « **Reply #17 on:** November 24, 2007, 02:59:58 PM »

I found that battery about a year ago and remember being impressed, but it was too big for my fish robot so I didn't get it . . .

It definitely makes using lithium batteries safer and easier . . .

s80ts0465 · « **Reply #18 on:** November 24, 2007, 03:53:14 PM »

yes it does.
Moreover it has the capacity of 3.6Ah or double with the add-on that i was looking for .
The doubt i've is around the charger, that isn't well described, but i'll send them an email just to know the carachteristic of the charger.
Moreover it would benice to know if is possible to change the battery after some time when it will die.

Ste

maverick monk · « **Reply #19 on:** November 24, 2007, 05:06:35 PM »

Quote from: s80ts0465 on November 23, 2007, 08:40:59 AM

i'm sorry to bug you

anyway here the datasheet : http://www.power-sonic.com/site/doc/prod/88.pdf

and it's wrote that for 1 hour rate the battery support 4.5A to 9V. The main trouble seems the drop to 9V !!!!

Anyway do you suggest me to use lithium battery even if i've to mantain almost always the battery connected to the charger ??

Bye

you will need a specific li-po charger, or else your battery will literaly explode. i would put the charger on a timer or voltage cut off meter, so it only begines charging again after a certain voltage drop

s80ts0465 · « **Reply #20 on:** November 25, 2007, 04:03:03 AM »

or better, i'll directly buy a new peak li-po charger

s80ts0465 · « **Reply #21 on:** November 29, 2007, 10:03:08 AM »

maybe i've found a problem of this lithium battery...it seems like the max output current is limited to 1.5A for 9V and 2A for 12V.
Could it be??

Admin · « **Reply #22 on:** November 29, 2007, 10:33:18 AM »

hmmmm yea, I didn't notice that before . . . ok don't get that battery . . .

s80ts0465 · « **Reply #23 on:** November 29, 2007, 10:40:52 AM »

i thought to have solved my problems

so i think i'll buy the classic NiMH battery pack.

But is it possible to charge this battery and at the same time use them??
i mean i should allow the robot to auto charge the battery without to switch it off; is it possible?? how??

Admin · « **Reply #24 on:** December 04, 2007, 02:36:55 PM »

Quote

But is it possible to charge this battery and at the same time use them??

yeap. it is just like using a laptop (that has a battery) while its plugged in.

s80ts0465 · « **Reply #25 on:** December 05, 2007, 08:11:58 AM »

What about this battery and charging connection??

is it correct or is it better to use another schema??? (the switch in the image is the on-offbotton that maybe i'll insert, but right now it's not in my plane.)

bye Bye Ste

Admin · « **Reply #26 on:** December 05, 2007, 08:27:50 AM »

hmmmm I don't see the charger in your schematic . . .

Just put the charger in parallel with your battery as if it was another battery.

s80ts0465 · « **Reply #27 on:** December 05, 2007, 01:31:48 PM »

ups i forgot to sign it. The right connector (typical) is the charger :-)

s80ts0465 · « **Reply #28 on:** December 08, 2007, 11:55:28 AM »

I'd have done my final choice.
Even if you tryed to avoid me to use a 24V motor i''ve decide to use one

. In fact after i've used your power calculator i noted that i can obtain good results only using a 24V motor.
So i'd have two pattery pack: one 24V for the motors and one 12V or 7.2V for all the rest.

I want to build a auto-docking and auto-charging robot, and i think that two different charger for each battery pack isn't a good idea.
Actually i think to buy only one 24V charger; to charge the 24 battery pack there is no problem, instead for the 12V or 7.2V battery pack i'd install on the robot a DC-DC switching converter to supply the correct voltage. I'd use the DE-SWADJ of DimensionEngineering :
http://www.dimensionengineering.com/DE-SWADJ.htm

Do you think could it work fine??

bye

Ro-Bot-X · « **Reply #29 on:** December 08, 2007, 01:06:24 PM »

If you use it just for electronics, it will work for sure (adjusted at 5V). If you need to also power servos, then use one of these for each couple of standard servos, adjusted at 6V. If the servos are high power, use one to each servo, or even 2 in parallel for each servo.

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Author Topic: Which battey for my robot ?? (Read 6442 times)

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